n-Gauge 1: Case Study 1

Beam Profile Reflectometry Measurement of Cardiac Stent Balloon Walls

The Task

n-eos was approached to use n-Gauge 1 to characterise the wall thickness of a representative set of cardiac balloons. The manufacturer wished to know whether the target thickness of 20μm was being achieved consistently. The balloons’ external dimensions, tubing, or ‘cone area’ that joins the tube to the balloon were not measured; however, n-Gauge 1 is easily capable of making these measurements, in conjunction with wall thickness, if required and configured to do so. All measurements were undertaken on deflated balloons as directed by the manufacturer. This made the shapes of the samples very irregular, greatly increasing the difficulty of the measurement for conventional techniques.

Sample Analysis and Results

The n-Gauge 1 system was first calibrated against a set of fused silica discs with thicknesses ranging from ~20μm to ~200μm. All samples were placed on a flat microscope stage and data collection initiated by adjusting parameters, focusing the laser beam onto the sample’s surface, and pressing a single button.

Measurements were made with no prior assumptions at all, measuring the thickness, refractive index, birefringence (related to stress in polymer films) and surface orientation at each point. The refractive index at the laser wavelength (640nm) was found to be stable at ~1.530 across the majority of measurement points. Results obtained are presented on the right, with W1 to W5 referring to the number of separate wall thickness measurements undertaken per balloon.

The results from each sample show a very consistent balloon wall thickness of ~20μm. No particular relationship between thickness and position along the balloons was noticed, except that there is usually less than a micron of variation along the length of the balloon and some balloons were consistently thicker than others. Typical data acquisition and calculation time at each point was about one second and three seconds respectively.

Conclusion and Outcome

Measuring the thicknesses of cardiac balloon walls on an n-Gauge 1 is simple, reliable and repeatable.

In this case study the manufacturer was able to use the quantitative and qualitative results obtained to quickly confirm the relative stability of their manufacturing process, and quality and reliability of their product.